Detection Capability

The amplitude of seismic waves decays with distance as they travel
through the Earth. This means we can only detect smaller earthquakes
at shorter distances. Also, we need to record the earthquake signal on
a number of sensors to make sure it is "real" and not just local
"noise".

Assuming that we need at least four stations to record a signal that
is twice the background noise level to be able to detect a seismic
event, then we can calculate what magnitude of earthquake we are able
to detect in different places for any set of seismic recording
stations.

The UK seismograph network is designed to detect nearly all magnitude
2.0 earthquakes in mainland UK. This means we are usually able to record any
earthquakes that are felt by people.